Isolation, expression, and functional analysis of the geranylgeranyl pyrophosphate synthase (GGPPS) gene from Liriodendron tulipifera

Isoprenyl diphosphate synthases of terpenoid biosynthesis in rose-scented geranium (Pelargonium graveolens)

The essential oil of Pelargonium graveolens (rose-scented geranium), an important aromatic plant, comprising mainly mono- and sesqui-terpenes, has applications in food and cosmetic industries. This study reports the characterization of isoprenyl disphosphate synthases (IDSs) involved in P. graveolens terpene biosynthesis. The six identified PgIDSs belonged to different classes of IDSs, comprising homomeric geranyl diphosphate synthases (GPPSs; PgGPPS1 and PgGPPS2), the large subunit of heteromeric GPPS or geranylgeranyl diphosphate synthases (GGPPSs; PgGGPPS), the small subunit of heteromeric GPPS (PgGPPS.SSUI and PgGPPS.SSUII), and farnesyl diphosphate synthases (FPPS; PgFPPS).All IDSs exhibited maximal expression in glandular trichomes (GTs), the site of aroma formation, and their expression except PgGPPS.SSUII was induced upon treatment with MeJA. Functional characterization of recombinant proteins revealed that PgGPPS1, PgGGPPS and PgFPPS were active enzymes producing GPP, GGPP/GPP, and FPP respectively, whereas both PgGPPS.SSUs and PgGPPS2 were inactive. Co-expression of PgGGPPS (that exhibited bifunctional G(G)PPS activity) with PgGPPS.SSUs in bacterial expression system showed lack of interaction between the two proteins, however, PgGGPPS interacted with a phylogenetically distant Antirrhinum majus GPPS.SSU. Further, transient expression of AmGPPS.SSU in P. graveolens leaf led to a significant increase in monoterpene levels. These findings provide insight into the types of IDSs and their role in providing precursors for different terpenoid components of P. graveolens essential oil.

The identification and functional characterization of the LcMCT gene from Liriodendron chinense reveals its potenatial role in carotenoids biosyanthesis

Terpenoids are not only important component of plant floral scent, but also indispensable elements in the formation of floral color. The petals of Liriodendron chinense are rich in tetraterpene carotenoids and release large amounts of volatile monoterpene and sesquiterpene compounds during full blooming stage. However, the mechanism of terpenoid synthesis is not clear in L. chinense. In this study, we identified a LcMCT gene and characterized its potential function in carotenoids biosynthesis. A total of 2947 up-regulated differentially expressed genes (DEGs) were discerned from the transcriptomic data of L. chinense petals, with a significant enrichment of DEGs related to plant hormone signal transduction and terpenoid backbone biosynthesis. After comprehensive analysis on these DEGs, the LcMCT gene was selected for subsequent function characterization. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) results showed that LcMCT was expressed at the highest level in the petals during full blooming stage, suggesting a possible role in carotenoids biosynthesis and volatile terpenoid biosynthesis. Subcellular localization showed that the LcMCT protein was localized in the chloroplast. Overexpression of LcMCT in Arabidopsis thaliana affected the expression levels of MEP pathway genes. Moreover, the MCT enzyme activity and carotenoids contents in transgenic A. thaliana were increased by 69.27% and 15.57%, respectively. These results suggest that LcMCT promotes the biosynthesis of terpenoid precursors via the MEP pathway. Our work lays a foundation for exploring the mechanism of terpenoid synthesis in L. chinense.

Two R2R3-MYB transcription factors from Chinese cedar (Cryptomeria fortunei Hooibrenk) are involved in the regulation of secondary cell wall formation

As the most abundant renewable energy source, wood comprises the secondary cell wall (SCW). SCW biosynthesis involves lignin and cellulose deposition. Increasing studies have illustrated that R2R3-MYB transcription factors (TFs) play pivotal roles in affecting lignin accumulation and SCW formation. Nevertheless, the regulatory roles of R2R3-MYBs are still unresolved in Cryptomeria fortunei Hooibrenk cambium and wood formation. To dissect the potentials of CfMYBs, we successfully cloned and intensively studied the functions of CfMYB4 and CfMYB5 in SCW formation and abiotic stress response. They both contained the conserved MYB domain capable of forming a special structure that could bind to the core motifs of downstream genes. The phylogenetic tree implied that two CfMYBs clustered into different evolutionary branches. They were predominantly expressed in the stem and were localized to the nucleus. Furthermore, CfMYB4 functioned as an activator to enhance lignin and cellulose accumulation, and increase the SCW thickness by elevating the expression levels of SCW-related genes. By contrast, CfMYB5 negatively regulated lignin and cellulose biosynthesis, and decreased SCW formation by reducing the expression of SCW biosynthetic genes. Our data not only highlight the regulatory functions of CfMYBs in lignin deposition but also provide critical insights into the development of strategies for the genetic improvement of Cryptomeria fortunei wood biomass.

Overexpression of Geranyl Diphosphate Synthase 1 (NnGGPPS1) From Nelumbo nucifera Enhances Carotenoid and Chlorophyll Content and Biomass

As the traditional herb with pharmacological compounds in China, the key genes related with terpenoid biosynthesis are still unveiled in Nelumbo nucifera. Geranylgeranyl pyrophosphate synthase (GGPPS) is one of the key enzymes in terpenoids biosynthesis, synthesizing the common precursor of GGPP for downstream enzymes for generating various terpenoids. In this study, four NnGGPPS genes were isolated from N. nucifera. Sequence and phylogenetic analyses indicate that NnGGPPS1 and NnGGPPS2 belong to large subunit (LSU). Whereas NnGGPPS3 and NnGGPPS4 are classified as small subunit (SSU) of SSU Ⅱ and SSU I, respectively. Among four NnGGPPSs, only NnGGPPS1 and NnGGPPS2 can produce GGPP in bacterial pigment complementation assay. Combination analysis of subcellular localization and gene co-expression analysis (GCN) illustrates that NnGGPPS1 is the main transcript related with methylerythritol phosphate (MEP) pathway, abscisic acid (ABA) biosynthesis, carotenoid and chlorophyll biosynthesis and degradation. Overexpression of NnGGPPS1 improves the growth of transgenic tobacco, and increases carotenoids and chlorophyll contents. Moreover, NnGGPPS1 transgenic tobacco exhibits improved photosynthesis efficiency and ROS scavenging ability. The up-regulated expression of the key genes in MEP pathway, carotenoid biosynthesis and chlorophyll biosynthesis, result in the increase of metabolic flux in NnGGPPS1 transgenic lines. Furthermore, the elevated MEP-derived primary metabolites of carotenoid and chlorophyll was attributed to enhancement of plant biomass of NnGGPPS1 transgenic lines. Therefore, NnGGPPS1 plays a vital role in biosynthesis of carotenoid and chlorophyll.

Identification and Functional Analysis of Two Novel Genes-Geranylgeranyl Pyrophosphate Synthase Gene (AlGGPPS) and Isopentenyl Pyrophosphate Isomerase Gene (AlIDI)-from Aurantiochytrium limacinum Significantly Enhance De Novo β-Carotene Biosynthesis in Escherichia coli

Precursor regulation has been an effective strategy to improve carotenoid production and the availability of novel precursor synthases facilitates engineering improvements. In this work, the putative geranylgeranyl pyrophosphate synthase encoding gene (AlGGPPS) and isopentenyl pyrophosphate isomerase encoding gene (AlIDI) from Aurantiochytrium limacinum MYA-1381 were isolated. We applied the excavated AlGGPPS and AlIDI to the de novo β-carotene biosynthetic pathway in Escherichia coli for functional identification and engineering application. Results showed that the two novel genes both functioned in the synthesis of β-carotene. Furthermore, AlGGPPS and AlIDI performed better than the original or endogenous one, with 39.7% and 80.9% increases in β-carotene production, respectively. Due to the coordinated expression of the 2 functional genes, β-carotene content of the modified carotenoid-producing E. coli accumulated a 2.99-fold yield of the initial EBIY strain in 12 h, reaching 10.99 mg/L in flask culture. This study helped to broaden current understanding of the carotenoid biosynthetic pathway in Aurantiochytrium and provided novel functional elements for carotenoid engineering improvements.

Volatile secondary metabolome and transcriptome analysis reveals distinct regulation mechanism of aroma biosynthesis in Syringa oblata and S. vulgaris

Lilacs have high ornamental value due to their strong aroma. However, the molecular regulatory mechanisms of aroma biosynthesis and metabolism in lilac were largely unclear. In this study, two varieties with distinct aroma, Syringa oblata 'Zi Kui' (faint aroma) and Syringa vulgaris 'Li Fei' (strong aroma), were used for exploring the regulation mechanism of aroma difference. Via GC-MS analysis, a total of 43 volatile components were identified. Terpene volatiles was the most abundant volatiles constituting the aroma of two varieties. Notably, 3 volatile secondary metabolites were unique in 'Zi Kui' and 30 volatile secondary metabolites were unique in 'Li Fei'. Then, a transcriptome analysis was performed to clarify the regulation mechanism of aroma metabolism difference between these two varieties, and identified 6411 differentially expressed genes (DEGs). Interestingly, ubiquinone and other terpenoid-quinone biosynthesis genes were significantly enriched in DEGs. We further conducted a correlation analysis between the volatile metabolome and transcriptome and found that TPS, GGPPS, and HMGS genes might be the key contributors to the differences in floral fragrance composition between the two lilac varieties. Our study improves the understanding in the regulation mechanism of Lilac aroma and would help improve the aroma of ornamental crops by metabolic engineering.

Functional verification and characterization of a type-III geranylgeranyl diphosphate synthase gene from Sporobolomyces pararoseus NGR

Carotenoids, a group of natural pigments, have strong antioxidant properties and act as precursors to vitamin A, which have garnered attention from industry and researchers. Sporobolomyces pararoseus represents a hyper-producer of carotenoids, mainly including β-carotene, torulene, and torularhodin. Geranylgeranyl diphosphate synthase (GGPPS) is regarded as a key enzyme in the carotenoid biosynthesis pathway. However, the precise nature of the gene encoding GGPPS in S. pararoseus has not been reported yet. Here, we cloned a cDNA copy of the GGPPS protein-encoding gene crtE from S. pararoseus NGR. The crtE full-length genomic DNA and cDNA are 1,722 and 1,134 bp, respectively, which consist of 9 exons and 8 introns. This gene encodes 377 amino acids protein with a predicted molecular mass of 42.59 kDa and a PI of 5.66. Identification of the crtE gene encoding a functional GGPPS was performed using heterologous complementation detection in Escherichia coli. In vitro enzymatic activity experiments showed that CrtE utilized farnesyl diphosphate (FPP) as an allylic substrate for the condensation reaction with isopentenyl diphosphate (IPP), generating more of the unique product GGPP compared to other allylic substrates. The predicted CrtE 3D-model was analyzed in comparison with yeast GGPPS. The condensation reaction occurs in the cavity of the subunit, and three bulky amino acids (Tyr110, Phe111, and His141) below the cavity prevent further extension of the product. Our findings provide a new source of genes for carotenoid genetic engineering.

Genome Sequencing of Amomum tsao-ko Provides Novel Insight Into Its Volatile Component Biosynthesis

As an important economic and medicinal crop, Amomum tsao-ko is rich in volatile oils and widely used in food additives, essential oils, and traditional Chinese medicine. However, the lack of the genome remains a limiting factor for understanding its medicinal properties at the molecular level. Here, based on 288.72 Gb of PacBio long reads and 105.45 Gb of Illumina paired-end short reads, we assembled a draft genome for A. tsao-ko (2.70 Gb in size, contig N50 of 2.45 Mb). Approximately 90.07% of the predicted genes were annotated in public databases. Based on comparative genomic analysis, genes involved in secondary metabolite biosynthesis, flavonoid metabolism, and terpenoid biosynthesis showed significant expansion. Notably, the DXS, GGPPS, and CYP450 genes, which participate in rate-limiting steps for terpenoid backbone biosynthesis and modification, may form the genetic basis for essential oil formation in A. tsao-ko. The assembled A. tsao-ko draft genome provides a valuable genetic resource for understanding the unique features of this plant and for further evolutionary and agronomic studies of Zingiberaceae species.

Cloning and homologous characterization of geranylgeranyl pyrophosphate synthase (GGPPS) from Withania somnifera revealed alterations in metabolic flux towards gibberellic acid biosynthesis

Overexpression of a novel geranylgeranyl pyrophosphate synthase gene (WsGGPPS) in planta resulted in increased levels of gibberellic acid and decrease in withanolide content. Withania somnifera (L.) Dunal, the herb from family Solanaceae is one of the most treasured medicinal plant used in traditional medicinal systems owing to its unique stockpile of pharmaceutically active secondary metabolites. Phytochemical and pharmacological studies in this plant were well established, but the genes affecting the regulation of biosynthesis of major metabolites were not well elucidated. In this study cloning and functional characterization of a key enzyme in terpenoid biosynthetic pathway viz. geranylgeranyl pyrophosphate synthase (EC 2.5.1.29) gene from Withania somnifera was performed. The full length WsGGPPS gene contained 1,104 base pairs that encode a polypeptide of 365 amino acids. The quantitative expression analysis suggested that WsGGPPS transcripts were expressed maximally in flower tissues followed by berry tissues. The expression levels of WsGGPPS were found to be regulated by methyl jasmonate (MeJA) and salicylic acid (SA). Amino acid sequence alignment and phylogenetic studies suggested that WsGGPPS had close similarities with GGPPS of Solanum tuberosum and Solanum pennellii. The structural analysis provided basic information about three dimensional features and physicochemical parameters of WsGGPPS protein. Overexpression of WsGGPPS in planta for its functional characterization suggested that the WsGGPPS was involved in gibberellic acid biosynthesis.

Transcriptomic profiling of the floral fragrance biosynthesis pathway of Liriodendron and functional characterization of the LtuDXR gene

Floral fragrance, which has the function of attracting pollinators, is a class of volatile secondary metabolites mainly released by the secretory tissue of petals. Terpenoids are key components of floral volatile substances. Previous studies have shown that there are significant differences in the concentration and composition of volatile floral fragrances, especially terpenoids, between Liriodendron chinense and L. tulipifera. At present, the mechanism by which the synthesis of floral fragrance is regulated in Liriodendron remains unexplored. In this study, we analyzed the differentially expressed genes (DEGs) of L. chinense and L. tulipifera, and identified 130 DEGs related to terpenoid synthesis. A KEGG enrichment analysis of DEGs related to terpenoid biosynthesis revealed that the monoterpenoid biosynthesis pathway was the most significant. We cloned the LtuDXR gene from L. tulipifera using RACE technology. RT-qPCR results showed that the expression of the LtuDXR gene was the highest in the early florescence petals, indicating that the LtuDXR gene may play a role in the synthesis of volatile terpenoids. Subcellular localization showed that the LtuDXR protein is mainly localized in the chloroplast. Overexpression of LtuDXR in Arabidopsis thaliana significantly increased the plant height, DXR enzyme activity, and carotenoid content. In this study, we identified and functionally characterized LtuDXR, which is involved in terpenoid synthesis in Liriodendron. Our work lays the foundation for further exploration of the molecular mechanism by which terpenoid biosynthesis is regulated in Liriodendron.